test: separate seam arming references from production crossings

[azimafroozeh]

What & why

Separate production seam crossings from test arming references in the catalog guard. The current check searches production source for both, so a crossing can satisfy the arming requirement even after the last test reference is removed.

Backing issue / RFC

Accepted issue or RFC link pending. This change does not qualify for the trivial fast-lane.

Checklist

• Change is focused (one logical change)
• Tests added/updated for behavior changes
• Public docs updated if user-facing surface changed (N/A; developer testing guide updated)
• Reviewed against architectural invariants; no Hard Invariant weakened or deny-list item hit

Local verification

• rustfmt --edition 2024 --check crates/omnigraph/tests/failpoint_names_guard.rs — passed
• git diff --check — passed
• python3 scripts/check-docs.py — passed, 142 Markdown files checked
• Existing guard tests compiled directly with rustc --test — 4 passed
• Full Cargo workspace tests and Clippy — not run; verification was limited to the source guard and documentation

Notes for reviewers

Production crossing detection excludes test files and inline test code. Arming references come from integration tests, in-source tests, the DST harness, and at: values in GQT --- seam sections.

The fixtures cover missing arming references, identifier boundaries, exact seam names, and source classification. A separate guard checks for overlapping file sets and installer calls in production text.

Four review findings remain unresolved: block-comment handling, cfg classification, installer-name false positives, and differences between the guard’s GQT extraction and the runner’s YAML parser.